I bought a solid Sterling Silver whistle on Ebay and worked it the same that I did on the brass one (filed a round hole on the belly, sanded and buffed). But this time, I rounded the air entrance (shaped it rather oval, from its flat rectangular profile) and included an extension in soft silicone that I sealed with a piece of heat-shrink tubing, used in electrical engineering. Thanks to the small ring at the bottom which provide a grip, the whistle gets totally hands-free!
The result is simply... stunning! The sound is very bright, clear and precise, the tone range is over-correct, and the whistle is quick as a lightning!! And it reacts very sensitively to any solicitations (tremolos and so). Incredible. Here is a sound sample which, despite my mediocre playing, is able to testify of the sound quality of this new baby.